1. Field of the Invention
The present invention relates to a ceramic electronic device, such as a multilayer ceramic capacitor, and the production method, and particularly relates to a ceramic electronic device having a low IR defect rate (initial insulation resistance defect rate), excellent high temperature load lifetime and high reliability and the production method.
2. Description of the Related Art
The multilayer ceramic capacitor is widely used as a highly reliable compact electronic device having a large capacity, and the number to be used in an electric apparatus and electronic apparatus is also large. In recent years, as apparatuses becoming more compact with higher performance, demands for a multilayer ceramic capacitor to be more compact, larger in capacity, lower in price, and higher in reliability have increasingly become stronger.
A multilayer ceramic capacitor is normally produced by stacking an internal electrode paste and a dielectric slurry (paste) by the sheet method or printing method, etc. and firing the result. Generally, Pd and a Pd alloy have been used for the internal electrode, but due to the high price of Pd, relatively in inexpensive Ni and a Ni alloy have come to be used. In the case of forming the internal electrode by Ni or a Ni alloy, there is a disadvantage that electrodes are oxidized when fired in the air. Therefore, after performing binder removal, it is generally fired under a lower oxygen pressure than an equilibrium oxygen partial pressure of Ni and NiO and subjected to thermal treatment thereafter to re-oxidize the dielectric layer.
However, when fired in a reducing atmosphere, there was a disadvantage that the dielectric layer was reduced and the insulation resistance (IR) becomes small. Therefore, a reduction-resistant dielectric material, which is not reduced even when fired in a reducing atmosphere, has been proposed (for example, the Japanese Unexamined Patent Publication Nos. 9-97734, 10-74666 and 2001-6966).
The Japanese Unexamined Patent Publication Nos. 9-97734 and 10-74666 disclose a dielectric layer having a segregation phase containing at least two kinds of oxides among an oxide of Li, oxide of Si and oxide of B. According to these articles, as a result that the segregation phase as above is included in a dielectric layer, a moving degree of electron moving in a grain boundary layer can be made lower and reliability under a high temperature and high voltage can be improved.
However, in the Japanese Unexamined Patent Publication Nos. 9-97734 and 10-74666, because the segregation phase contains an oxide of Li, Li2O vaporizes easily, voids (air-gaps) are generated easily, it is affected by temperature, and ion migration is easily caused, so that an affect of improving the high temperature load lifetime is insufficient. Also, in these articles, the IR defect rate (initial insulation resistance defect rate) is not improved, so that there are concerns that the IR defect rate declines when the dielectric layer is made thin.
Also, the Japanese unexamined Patent Publication No. 2001-6966 discloses a dielectric layer having a segregation phase (secondary phase) containing at least a rare earth and, furthermore, a glass component, wherein SiO2 or B2O3 is the main component. According to the article, a ceramic capacitor having excellent lifetime characteristics and whether resistance can be obtained even if fired in a reducing atmosphere.
However, in the Japanese Unexamined Patent Publication No. 2001-6966, the inventors clearly describes that there is a disadvantage that the IR defect rate becomes high when it is made to be thin as 4 μm or thinner because B (boron) is used and the composition of grain boundary becomes uneven.